734 
CHEMISTR V OF RESPIRA TION. 
In 1834, Theodor Schwann 1 showed that, when hens' eggs are kept at a 
warm temperature in gases containing no oxygen, the germinal membrane 
enlarges, and the area pellucida is formed, but no embryo ; eggs would develop 
normally in warm air, after they had been in hydrogen for twenty-four hours at 
a warm temperature, but not if the exposure to hydrogen had lasted thirty 
hours or more. 
The first determinations of the respiratory exchange in eggs are due to 
Baudrimont and Martin Saint-Anges, 2 who showed that the eggs of birds and of 
snakes gave off carbon dioxide during incubation, and that the embryos of 
frogs died if placed in water free from air. The quantitative results obtained 
by these observers are not trustworthy, owing to the defective methods of gas 
analysis then in use. The first reliable determinations are those made by 
Baumgartner 3 throughout the period of incubation of hens' eggs. The follow- 
ing table gives some of the results : — 
Day of 
Incubation. 
Loss of Weight of Ego. DlSCI ' 0,™°***°* 
Absorption of Oxygf,n. 
From the 
commencement of 
incubation. 
On the day in 
question. 
For one 
egg- 
For one kilo, 
of eggs. 
For one 
egg- 
For one kilo, 
of eggs. 
Grms. 
1 
9 1-853 
20 10-479 
21 
(chick free) 
Gnus. 
125 
0-164 
0-212 
Grms. 
0-009 
0-048 
0-560 
1-008 
Grms. 
0-16 
1-01 
18 '93 
Grms. 
0-0074 
0-0360 
0-4435 
0-7317 
Grms. 
0-13 
0-76 
14-90 
Similar experiments were made by Pott and Preyer, 4 who found that a fertile 
egg, weighing 50 grms., lost in weight about 10 - 27 grms. during incubation, an 
unfertile one 9-70 grms., and an egg kept at the temperature of an ordinary 
room P66 grms., in twenty-one days. The respiratory exchange of a developing 
embryo in an egg weighing 50 grms. was, fur periods of twenty -four hours : — 
Day of Incubation. 
Discharge of Carbon Dioxide. 
Absorption of Oxygen. 
7 
13 
21 
Grms. 
0-09 
0-24 
0-86 
Gnus. 
0-09 
0-24 
0-68 
Pott r ° also showed that the development of the embryo is not hastened or 
delayed if the egg is incubated in an atmosphere of oxygen. During incuba- 
tion, it has been proved that the temperature of the embryo, owing to its meta- 
bolism, is slightly warmer than the temperature of its surroundings. 
1 Arch. f. Anat., Physiol, u. icissensch. Med., 1835, S. 121. 
2 Compt. rend. Acad. d. sc, Paris, 1843, tome xvii. p. 1343; Ann. dc chim. et phys., 
Paris, 1847, Ser. 3, tome xxi. p. 195. 
3 " Der Athmungsprozess im Ei," Freiburg im B., 1861. 
4 Arch. f. d. yes. Physiol., Bonn, 1882, Bd. xxvii. S. 320. 
5 Ibid,, 1S83, Bd. xxxi. S. 268. 
6 Biirensprung, Arch. f. Anat., Physiol, u. icissensch. Med., 1851, S. 126. See also 
'• Animal Heat," this Text-book, vol. i. 
